Irradiation intensity independence

A prerequisite for the evaluation mentioned is knowledge about the reaction mechanism. Linear absorbance diagrams proved the photoisomerisation taking place as in solutions. However, the siloxane matrix has to be fresh. Different types of siloxanes were tested, some photochemically polymerised, others fabricated by a catalyst induced process. In the latter case the Pt-catalyst must not overcome a concentration limit otherwise it influences the azobenzene photoreaction. Approximate evaluations at low absorption (assuming a irradiation intensity independent of the volume element) do not offer appropriate results because of measurement problems. Therefore a transformation of the time scale has been used, discussed in Section 5.7.3. 

Transient spectra showed that these benzophenone phosphorescence decays were due only to the benzophenone triplet , and the irradiation intensity independence ruled out the T-T annihilatitm under the experimental conditions used Since the deviation was not observed at temperatures below T of each acrylic polymer or T of polystyrene and polycarbonate, this quenching is considered not of the static character as featured in the Inokuti-Hirayama theory, but of a dynamic type associated with the collision of functional groups and the energy transfer with some activation energy. 

Radiation-induced oxidation of alcohols is a non-chain reaction when the temperature is sufficiently low and kp/ /2kt < /H /[RH]. In this case, the reaction rate is proportional to the irradiation intensity (/) and is virtually independent of temperature [46,63—69]. 

As derived in Example 3.13 the mechanism of a photoreaction sensitised by radicals results in a quantum yield dependent on concentration and on intensity of irradiation. One finds according to eqs. (3.10) and (3.36) for the intensity independent factor Z ... 

The concept of impedance is only applicable if the system under study complies with the conditions of stability, causality, finity, and linearity. It is good practice to verify whether these conditions hold before giving further interpretation to the data. A stable Systran has a Zfym) independent of time. Causal systems do not show any response if the input signal is zero (in the dark for IMPS). All practical systems are finite. Linear systems show a response linearly related to the input the current density is hnearly related to the irradiation intensity. A convenient technique... 

In the case of irradiation-induced chemical ageing, e.g. radio- and photooxidation, Cg and D are light intensity independent (Equation [12.60] remains valid). At the opposite, it can be demonstrated that the effect of light intensity I on Ts can be satisfyingly approximated by a simple power law ... 

For a parallel monochromatic radiation beam, where the proportion of radiation absorbed by a substance is independent of the intensity of the incident irradiation, i.e. the probability of absorption is linearly dependent on incident intensity, which is the usual case for single photon transitions, each successive layer of thickness dr absorbs an equal fraction —dl/I of radiant intensity /, and integration across a finite thickness, x, with an initial irradiation intensity Iq gives ... 

Thus for an ideal two-phase system the total calibrated intensity that is scattered into the reciprocal space is the product of the square of the contrast between the phases and the product of the volume fractions of the phases, Vi (1 — Vi) = V1V2. V1V2 is the composition parameter66 of a two-phase system which is accessible in SAXS experiments. The total intensity of the photons scattered into space is thus independent from the arrangement and the shapes of the particles in the material (i.e., the topology). Moreover, Eq. (8.54) shows that in the raw data the intensity is as well proportional to the irradiated volume. From this fact a technical procedure to adjust the intensity that falls on the detector is readily established. If, for example, we do not receive a number of counts that is sufficient for good counting statistics, we may open the slits or increase the thickness of a thin sample. 

The Maxwell-Heaviside theory seen as a U(l) symmetry gauge field theory has no explanation for the photoelectric effect, which is the emission of electrons from metals on ultraviolet irradiation [39]. Above a threshold frequency, the emission is instantaneous and independent of radiation intensity. Below the threshold, there is no emission, however intense the radiation. In U(l), electrodynamics energy is proportional to intensity and there is, consequently, no possible explanation for the photoelectric effect, which is conventionally regarded as an archetypical quantum effect. In classical 0(3) electrodynamics, the effect is simply... 

Martin (Ref 5) obtd an expin temp of 245° for 0,02 g of the subst which detond violently after 5 sec, but this compd could not be detond by impact. The photochemical decompn of Na, K Li azides in solns irradiated by UV light of 2537-Xwave length was studied by Bonnemay (Refs 13), For low concns the reactn was homogenous and decompn proceeded at a vel proportional to the conen, but independent of the cation. At high concns the vel of decompn was not explained by a simple law (for example Beer s Law) but showed, after an induction period, that reaction proceeded by chains which formed at the start of photolysis. Crystalline Li azide can be initiated to expln by intense electron streams but not by slow neutron bombardment (Ref 16)... 

The (chemical) actinometer A (Figure 7.40), is a photo reactive sample of known quantum yield a. For the determination of the quantum yield of the unknown sample S, this sample and the actinometer are irradiated simultaneously through the beam splitter B, which divides the incoming beam in a ratio rA, which is independent of time and of light intensity. The change of concentration, Ac(A), of the actinometer gives the number of photons absorbed, so that the quantum yield of the unknown reaction is obtained as the ratio of the concentration changes... 

The quantum yield of the primary hydrogen abstraction process is unity, and is independent of irradiation wavelength, light intensity and temperature. Its wavelength range follows of course the absorption spectrum of anthraquinone so that this actinometer is particularly well suited for the UV region. 

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